Align the site with the 6.0.0 dataset: re-point download links and sizes, drop stale references

[gsvgit]

dev works towards v6.0: the dataset on S3 is at the 6.0.0/graph/ prefix (self-contained archives), but the site still points at 5.0.0 artifacts. No package version bump in this task (that happens in the rename task, 49) — this is preparation: make all site references consistent with the 6.0.0 dataset.

• Re-point every download link from 5.0.0/graph/ to 6.0.0/graph/: the 113 per-graph pages (docs/graphs/data/*.rst, "Direct download") and the eight category tables (docs/graphs/*.rst, "Download" column).
• Update the Size (MB) columns against the 6.0.0 archives with utils/archive_sizes.py --update (sizes differ, e.g. xz_field_sensitive_alias 27.7 KB -> 536 KB); verify with the check mode afterwards.
• docs/utils.rst: update the current-state prefix references to 6.0.0/graph/ (upload key example, archive_sizes coverage description, --audit example). The migrate_gdrive_to_s3 section describes the historical migration — leave it untouched.
• AGENTS.md "Package layout": cfpq_data/dataset/ no longer has download_grammars/download_benchmark (removed in 48-S6) — fix the line to match the current API (download, reachable_pairs).
• Benchmark page related stuff stays removed from dev: do not re-introduce any benchmark page or reference as part of this alignment. Historical changelog entries and the flpq.rst design references stay; LICENSE-DATA.txt keeps "benchmarks" because the 4.0.0/benchmark/ data is still distributed.

Verification: utils/archive_sizes.py (check mode) passes; no 5.0.0/graph link remains in docs/ outside historical text; docs build green.

[gsvgit]

Detailed Plan: Issue #133 — Align the site with the 6.0.0 dataset

Context

dev works towards v6.0 (user decision: preparation only, no version bump —
that is task 49). The dataset on S3 is at the 6.0.0/graph/ prefix
(self-contained archives), but the site still points at 5.0.0 artifacts: all
226 download links (113 per-graph pages + 113 category-table rows) use
5.0.0/graph/, the Size (MB) columns reflect 5.0.0 archive sizes, and
docs/utils.rst / AGENTS.md carry stale references. The 6.0.0 archives
have different sizes (e.g. xz_field_sensitive_alias: 27.7 KB -> 536 KB).

Scope per the issue: re-point links, refresh sizes via the existing tool,
update the two stale reference spots, and keep benchmark page related stuff
removed (no re-introduction; historical changelog entries and flpq.rst design
references stay; LICENSE-DATA.txt keeps "benchmarks" because the
4.0.0/benchmark/ data is still distributed). The old-graphs table links to
4.0.0/graph/ and stays untouched.

Subtasks

S1: Re-point all download links to 6.0.0/graph/ [done] 467fe08

Code: none (docs-only)
Tests: skip (no code); verify with a grep that no 5.0.0/graph link
remains in docs/graphs/ and that the old-graphs table still points at 4.0.0
Docs: docs/graphs/data/*.rst (113 "Direct download" links) and
docs/graphs/*.rst (8 category tables, 113 "Download" links)

Spec:

• Replace every https://cfpq-data.storage.yandexcloud.net/5.0.0/graph/
  with https://cfpq-data.storage.yandexcloud.net/6.0.0/graph/ in the 121
  files (226 links). No other text changes.

S2: Refresh the Size (MB) columns against the 6.0.0 archives [done] 271861f

Code: none (tool-driven docs update)
Tests: utils/archive_sizes.py check mode must pass after the update
Docs: the Size (MB) cells of the eight category tables in
docs/graphs/*.rst (the tool rewrites only drifted cells)

Spec:

• Run uv run python utils/archive_sizes.py --update (anonymous HTTP HEAD
  against the public bucket; no credentials).
• Verify with check mode (exit 0) and inspect the diff: only size cells of
  the 6.0.0-re-pointed tables change; the old-graphs (4.0.0) table is
  untouched.

S3: Update stale prefix references in docs/utils.rst and AGENTS.md [done] a94b8bd

Code: none (docs-only)
Tests: skip (no code); docs build green
Docs: docs/utils.rst (upload key example, archive_sizes coverage
description, --audit example), AGENTS.md ("Package layout")

Spec:

• docs/utils.rst: current-state references move to 6.0.0/graph/ — the
  upload --key example, the archive_sizes coverage sentence ("113 archives
  at the ... prefix"), and the --audit --prefix example. The
  migrate_gdrive_to_s3 section describes the historical migration (5.0.0) —
  leave it untouched.
• AGENTS.md "Package layout": the cfpq_data/dataset/ line still lists
  download_grammars/download_benchmark (removed in 48-S6); replace with the
  current API (download, reachable_pairs).